There have been proposed many methods for producing porous cast iron, for example, U.S. Pat. No. 2,763,583 disclosed that if a cast iron is alternately and repeatedly subjected to heating up to a temperature of its A.sub.1 transformation point and cooling to an ambient room temperature, the cast iron becomes porous because the phenomenon of expansion of the volume of graphite contained in the cast iron i.e., the phenomenon of the so-called "growth" of the graphite takes place together with the phenomenon of "growth" of the cast iron and then the phenomenon of cracking along the graphite takes place.
It is also well known that the porous cast irons thus obtained are excellently permeable with oil and are useful for machine parts, for example, such as bearings.
There is also disclosed in Japanese Patent Nos. 276,978 and 620,648 that aluminum or tellurium is added to the cast iron in order to increase oil content or to decrease the number of times of the heat treatment due to the increase of growth rate.
However, there have been defects in the conventional methods for producing the porous cast iron in that repeatedly heating and cooling the cast iron take a long time for the heating and cooling treatment.